A completely reliable and adjustable trigger assembly for semi-automatic rifles (i.e., those that automatically cock their triggers after each firing, allowing successive rounds to be fired by repeatedly pulling the trigger) has long been sought by gunsmiths. For example, the Model 10/22 rifle was introduced by RUGER in 1964, and gunsmiths have made countless modifications to the stock trigger assembly during the ensuing years. The trigger, hammer and sear for this rifle have been repeatedly redesigned and manufactured from exotic materials, such as A-2 tool steel, T6 6061 aluminum and titanium, yet no one has achieved a trigger assembly of match quality. In the past, no nationally recognized shooter or gunsmith has thought it possible to compete against bolt action rifles (i.e., rifles that do not automatically cycle), with their superior triggers, using a semi-automatic rifle.
As illustrated in FIG. 1, the RUGER 10/22 rifle trigger assembly, indicated generally at 10, is a single stage trigger assembly. The trigger assembly 10 includes a trigger 12 that pivots at trigger pivot pin 14, a trigger return spring 16, a sear 18, which independently pivots on the pivot pin 14, a safety 20, a disconnector 22 pivoting on the trigger 12 at pin 24, a hammer 26, and a mainspring 28.
In operation, the hammer 26 is cocked, thereby engaging sear hook surface 30 with the hammer hook surface 32. Pulling back on the trigger 12 causes movement of disconnector 22, which in turn causes movement of sear 18. After pulling the trigger 12 a great enough distance, sear 18 has moved far enough to cause disengagement of the hook surfaces 30 and 32, thereby allowing the compressed mainspring 28 to push the hammer 26 into its firing position.
This single stage trigger assembly 10 requires a pull weight of six (6) to eight (8) pounds (on average) to fire. This pull weight is established by the mechanical linkage of the various parts of the trigger assembly 10, and is not adjustable. Also, the hammer-to-sear engagement is not adjustable, and in order to remove the factory creep, the hammer hook surface 32 must be reduced for less engagement with the sear 18. Unfortunately, such modification drastically reduces the reliability of the trigger assembly 10, as the sear 18 will not always engage with the modified hammer 26, causing the rifle to fire unexpectedly.
Finally, the trigger assembly 10 does not incorporate an overtravel stop, which stops the rearward movement of the trigger 12 once the hammer 26 is released by the sear 18. All of the above factors conspire to make the trigger assembly 10 inadequate for match competition.
A more suitable trigger assembly for match competition is marketed by WALTHER under the name GSP and is illustrated in FIG. 2 and indicated generally at 50. The trigger assembly 50 includes a trigger 52, trigger bar 54, sear 56, hammer 58, first stage travel adjustment screw 60, trigger bar engagement screw 62, trigger stop 64, length of pull adjustment screw 66, adjustable first stage weight plunger 68, adjustable second stage weight plunger 70, sear (second stage) engagement screw 72 (sets let-off point), and lock down screw 74 (to secure trigger assembly 50 to the rifle).
The trigger assembly 50 is a two stage trigger. As the trigger 52 is pulled back, it initially encounters resistance from the first stage weight plunger 68, but does not contact the second stage weight plunger 70. Further travel of the trigger 52 eventually encounters resistance from the second stage weight plunger 70 (in addition to the resistance already being provided by the first stage weight plunger 68). The effect perceived by the user is that the trigger 52 pulls back smoothly until the point where the second stage weight plunger 70 comes into play. Thereafter, greater force must be applied to move the trigger 52. If the position of the second stage weight plunger is chosen to coincide with a sear 56 position just prior to hammer 58 release, the shooter may squeeze the trigger 52 until the additional pressure is felt, knowing that any further incremental pull of the trigger 52 will cause the gun to fire. This is a very advantageous trigger operation for precision shooting, such as in match competition.
Even with these improvements, problems still exist in these prior art designs. Perhaps greatest is that the WALTHER GSP requires more than three (3) pounds of pull on the trigger 52 in order to overcome the resistance of the first and second stage weight plungers 68, 70. Such required pull forces create relatively high pressures between the rifle and the shooter's hand, leading to unacceptable inaccuracies in the aiming of the rifle.
There is therefor a need for a trigger assembly for a semi-automatic rifle that is suitable for match competition. The present invention is directed toward meeting this need.